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Can a Furnace Unit be Oversized?

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Can a Furnace Unit be Oversized?

Posted On: March 18, 2025

Can a Furnace Unit be Oversized?

a furnace can absolutely be oversized, and it’s a more common problem than you might think. While it may sound like having a more powerful furnace is a good thing, an oversized unit can actually cause several problems for your home’s comfort and efficiency.


Signs Your Furnace Might Be Oversized

  1. Short Cycling — The furnace turns on and off frequently because it heats the space too quickly, shutting off before completing a full heating cycle. This leads to uneven temperatures and increased wear on the unit.


  2. Uneven Heating — Some rooms may feel too warm, while others stay cold because the heat doesn’t distribute evenly before the system shuts off.


  3. High Energy Bills — Short cycling uses more energy since the furnace draws the most power during startup. Constantly restarting increases your energy costs.


  4. Excessive Wear and Tear — The repeated on/off cycling causes parts to wear out faster, leading to more frequent repairs and a shorter lifespan for the unit.


  5. Poor Humidity Control — Furnaces also help control humidity levels in your home. An oversized unit doesn’t run long enough to properly remove moisture from the air, leaving you with a clammy, uncomfortable environment.



What Causes an Oversized Furnace Installation?

  • Improper Load Calculation — If the HVAC contractor didn’t properly calculate your home’s heating load (taking into account square footage, insulation, windows, etc.), they may have installed a larger furnace than necessary.
  • "Bigger is Better" Mentality — Some people assume a larger furnace will heat the home faster, but this actually leads to inefficiency and discomfort.
  • Old House Upgrades — If you’ve added insulation, replaced windows, or improved energy efficiency, your original furnace may now be oversized for your current needs.

How to Fix an Oversized Furnace

  • Replacement — The most effective fix is replacing the unit with one properly sized for your home. An HVAC professional can perform a Manual J Load Calculation to determine the right size.
  • Adjustments — In some cases, technicians can modify the blower speed or adjust gas pressure to reduce output, but this is more of a temporary fix.
  • Zoning Systems — If replacement isn’t an option, installing a zoning system can help direct heat to specific areas more effectively.


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See What Our Customers Are Saying:

by Private User from Private User on Twintech Heating and Cooling

I have used Twintech many times over the years. They always arrive quickly and get the issue fixed. The most recent incident was when my air conditioner broke last week I called Greg at 11:30am and he was at my home by 2:30pm he had the unit fixed by 3:30pm. Twintech are very reliable and honest and they are experts in the field. I have already recommended them to many of my friends. I would not use anyone but them for my heating and air conditioning issues.

by Kate A in Pickering on Twintech Heating and Cooling

I would highly recommend these guys, professional, fast and competitive pricing. I moved into this place with no working AC unit with a 8 month baby, he was able to come with in a week to fix even in the busy summer days. He really values his customers , I am already recommending to my neighbors.

by Private User in Whitby on Twintech Heating and Cooling

Very impressed they arrive to quote even though I had forgotten to call them back to confirm date & time. They showed the day before installation to deliver the unit. Returned the next day as promised at 9am. Project was completed in a professional manner. They even fixed a few things that they noticed were not installed correctly, or to code by previous heating & air contractors we had at our residence before. Would recommend this company to everyone!

by Private User from Bowmanville on Twintech Heating and Cooling

Greg removed old oil furnace and oil tank from basement relocated new Napoleon propane furnace to allow duct work to be rerouted to a much more suitable location. Moved air conditioner to the new furnace. Dave recommended two available grants to assist with cost. They kept to their original quoted price which was substantially lower than a competitors for the same furnace and work. They completed the work as stated when stated and left the area clean and tidy. We are very pleased with the outcome.

by astephenson in Oshawa on Twintech Heating and Cooling

Twintech installed a Goodman furnace and ac init. Very professional install, both units are working well.

by rcnichols electric in Whitby on Twintech Heating and Cooling

We had Grant and Greg Dainty quote to replace our 20 yr old furnace. I have known them for years and have had other jobs done by them ( AC and Pool Htr). The price was very reasonable and the job was completed in one day.

by Rick. F. in Pickering on Twintech Heating and Cooling

TwinTech was the right choice. Our consultation with Dave set the tone. Professional and knowledgeable, we even received a follow-up call within hours of our install completion, wow! TwinTech arrived as scheduled to install our A/C unit. Within minutes of arrival Greg noted and explained a few out of code faults on our furnace installed by another company, problems fixed, thanks TwinTech. Greg, Grant and "Subaru" Pete were meticulous start to finish. Highly recommended!

by Taresh, Pickering on Twintech Heating and Cooling

Twintech replaced our aging +20 yrs old Furnace & AC with the variable high efficiency Napoleon Furnace matched with the Goodman AC. Sales guy ,Dave was great, gave a no pressure estimate, explained about the Government Rebate program which they took care of completely including arranging the home energy audit. On the scheduled day Greg and his team arrived on time, did a great job and completed the same day , extremely professional and courteous, cleaned up everything , tested the system, Greg took his time to explain the setup. Very impressed with the Napoleon Furnace 9600 which did a great job in maintaining a comfortable temperature last winter and now with the hot weather the Goodman AC cooled the house in much less time than the old AC unit could ever. From start to finish Twintech were great and have no hesitation in recommending them 100%.

by Private User Pickering, ON on Twintech Heating and Cooling

The Twintech team did an excellent job installing our new Goodman air conditioner. They were polite and professional. Greg was knowledgeable and clearly experienced. Thank you Twintech for bringing our cooling system up to current regulations. Job well done!

by Y. M. from Pickering on Twintech Heating and Cooling

Dave from TwinTech was very knowledgeable, professional and thorough in the buying process. He helped us to identify the best furnace for our home and our budget. When we needed a new filter a year later and seemed to have a problem finding the right one, I called Dave up and he delivered a filter to me the next day! The cost was on par with other retailers, but it was this unexpected personal service that really was impressive. The furnace? Works like a charm.

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See What Our Customers Are Saying:

by Aaron on Twintech Heating and Cooling

We are very happy to recommend this company to everyone. Our furnace broke down on Sunday morning. We phoned them and before noon Grant the owner showed up. He worked on the furnace for about a hour not wanting to give up to fix the problem. The furnace was 17 years old. I was the one talking about replacing it. End result was the next day it was all done. On the Sunday Bob came over with heaters to warm up the house. We decided to replace the water heater at the same time. Thanks Grant for the excellent work. Thumbs up.

by Linda on Twintech Heating and Cooling

Right on time. Explained how to work the HRV in a different way so the house would not be so dry. Changed my whole house water filter for me as well. Friendly, helpful, caring service!

by Robert Rogers on Twintech Heating and Cooling

Very pleased with the professional service that TwinTech Heating and Cooling provided in replacing my furnace. I got several quotes from different service providers. Their price was excellent and they explained the features very well. We are very glad we went with TwinTech and highly recommend their services.

by Robert Mizuno on Twintech Heating and Cooling

We were new homeowners in need of a second opinion. TwinTech Heating & Cooling were Amazing and professional. Very knowledgeable and great service all around. Recommend to anyone looking for honest and reliable services. Treated with respect and care. Thank you Greg, Mitch and Bob!

by Ruth on Twintech Heating and Cooling

TwinTech is an excellent and honest company! I called them for a second opinion after being told by another company that I needed to replace my furnace. Turns out this was not the case at all! I did not need a new furnace. TwinTech did not push to make an unnecessary sale and saved me from a huge expense. Bob and Mitch were extremely professional and above all honest! I definitely recommend TwinTech!

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